As already known, the so called “American coffee” is an infusion made by means of a particular machine wherein the hot water passes through a filter containing ground unpressed coffee and settles by gravity in an underlying pot.
The coffee used for the preparation of such a drink is different from the one used by mocha machines or machines for Italian espresso because it is more roughly ground and it is not subjected to any pre-compression when it is in the capsule.
Some machines, which are presently commercially available, have been expressly designed for the preparation of American coffee and are characterized by a very simple operation.
In fact, these machines have a water tank, a pump sending heated water inside a small container provided with a paper filter containing coffee. The hot water submerges the coffee and, passing through the paper filter, falls by gravity into the dedicated underlying pot which is suited to keep the drink hot for a long time because it is heated by a special electrical resistance.
Besides traditional American coffee machines, wherein the cone-shaped filter is manually filled by the user, capsules having an outer casing containing a paper filter partially filled with unpressed coffee have recently appeared on the market.
By means of suitable percolator machines, the plastic lid and the plastic bottom are pierced in order to create a hot water flow infusing the coffee powder.
However, the capsules which are presently commercially available are not completely reliable. In fact, since they usually have only one filter in the bottom, the incoming hot water is induced to flow along substantially vertical preferential fluid threads which, therefore, do not involve the whole mass of powdered product contained in the capsule.